1. Field of the Invention
The present invention relates to a helicopter mast which may be temporarily removed to effect the compact storage of a helicopter and, more particularly, to a helicopter mast which may be taken off of the helicopter body together with the encased drive shaft, the rotor hub, and part of the blade pitch control linkage, by removing expandable bushing bolts.
2. Description of the Prior Art
A helicopter is ofttimes transported by airplane or seagoing ship to a distant location where it is to be used. As cargo space is always at a premium aboard the transporting airplane or ship, such transport will typically involve partial disassembly of the helicopter for more compact storage. Especially when the helicopter is to be used for military purposes, it is desirable that the helicopter be easily and quickly reassembled at the destination, preferably without the aid of heavy or complex equipment which must also be shipped to the reassembly location.
The main rotor blades extend radially from a rotor hub which, in turn, is mounted on and rotates about a mast that projects vertically from the helicopter body. The blades are quite long, greatly exceeding the width of the helicopter body, and extend radially from and approximately perpendicularly to the vertical mast. The foregoing operational configuration of the helicopter requires much more storage space than the actual volume that it occupies, makes moving the helicopter in a confined area cumbersome, and exposes the main rotor blades to damage while the helicopter is being moved and during storage.
An approach that has been used in response to this problem has been to fold each of the helicopter's main rotor blades about a hinge in the blade or in the hub. For example, U.S. Pat. No. 5,211,538 issued to Seghal et al., describes folding the main rotor blades about hinges in the blades; while U.S. Pat. Nos. 5,322,415 issued to White et al., and 5,249,926 issued to D'Anna et al., show folding the main rotor blades about hinges located in the hub.
Although the foregoing design reduces the necessary storage space, the mast still projects from the helicopter body when the blades are folded. The projecting mast takes up vertical space and remains exposed to damage. Moreover, folding requires that a hinge be incorporated into each blade or into the respective junctions between the hub and each blade. Such structure adds mechanical complexity, weight and cost to the main rotor blades.
When the blades are straightened, the hinges must be securely locked to ensure that the straightened blades have the rigidity required to generate the lift and control characteristics essential for flight. Furthermore, the folding, unfolding, and locking of each blade may introduce displacements. Such displacements deleteriously affect the precise alignment and functional interactions of the mechanical elements of the blade pitch control system, and thereby degrade the control system's accuracy. Most obviously, the folded blades remain mounted on the helicopter mast during loading, transit, and unloading, thus remaining exposed to damage through accident, negligence or sabotage.
Another approach has been to remove the blades from the hub and store them separately. This avoids some of the problems related to folding the blades. However, the mast still projects from the helicopter body even after the blades have been removed, taking up valuable cargo space. Furthermore, the projecting mast remains exposed to damage during loading, transit, and unloading.
Removing the main rotor blades from the mast and the mast from the helicopter body has also been tried. The mast has heretofore been attached to the helicopter body by threaded bolts which circle the annular base of the mast and are aligned parallel to the mast's centerline. This resolves most of the previously mentioned problems, but at the considerable sacrifice of several of the primary criteria for reassembly, namely, ease and speed. The difficulty lies in complying with the exacting torque specifications required to ensure the proper tension in each of the plurality of bolts which ring the base of the mast.